Bait stores may sell them. SO far the few places i found info about them (such as the wormman site I posted earlier) use farmed worms. I suspect they won't be fed on dead animals and stuff. Apparently that can poise a health risk (saw some articles about it) so I suspect farmers who produce these worms use some sort of clean disease free area. Probably bred and fed in compost type setups. I haven't found info about how to breed them so not sure what they use.
Emailing suppliers about them should give you more information about how the spikes are raised/bread. May take some hunting but it can be done.
I suggest checking with your local bait shops, especially if you are near any popular fishing areas. I believe these are used for pan fish, maybe trout as well. If you live in an area with good spots to get pan fish or trout such as rainbow, the bait shops may have these too. I recommend not getting the colored ones. Not sure what they use to die the maggots different colors, (white is natural) so don't know if they are potentially harmful to dragons or other reptiles. IF a natural food die, then it should be fine.
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PHLdyPayne